Thixotropic,non-sag,one-coat paints containing binary mixtures of oil modified alkyds having different oil lengths



Oct. 28, 1969 w, EL IS ETAL 3,475,360

TI-IIXOTROPIC, NON-SAG, ONE-COAT PAINTS conmnune BINARY MIXTURES OF OILMODIFIED ALKYDS HAVING DIFFERENT OIL LENGTHS Filed July 1, 1965VISCOSITIES OF SOLUTIONS OF RESIN PAIRS RESIN 4 IN RESIN 6 I!) U X I9100 L 5 nasm s 1 IN RESIN 4 C 3 so 8 RESIN 5 m RESIN e o I l l 0 2o 40so so 10o WEIGHT PERCENT,OF FIRST RESIN I IN BLEND WITH SECOND RESININVENTORS WILLIAM H. ELL/5' I EARL F. CARLSTON {IT e00 Baooxs ATTORNEYSUnited States Patent US. Cl. 260-22 8 Claims ABSTRACT OF THE DISCLOSUREOil-based paints having as non-volatile vehicles, binary mixtures of oilmodified alkyd resins having different oil lengths, the interactionbetween the resins imparting nonsag and thixotropic properties to thepaints.

The present invention relates to one-coat, non-sag, thixotropic, paintsand as bases for the paints, non-volatile vehicles which are binarymixtures of certain oil-modified alkyd resins or mixtures of the resinsand drying oils. The vehicles are especially useful in preparinghigh-gloss enamels.

In the paint art, it has been found highly advantageous to employone-coat paints. It is obvious from the point of economy that the use ofa paint which will provide adequate coverage of surfaces with one coatwill reflect substantial savings in labor and materials over the use ofordinary paints, which often require two or more applications. One-coatpaints are defined in the art as those that have suflicient hiding powerto cover any color of surface in one application by brush, roller orspray. In the case of enamels, the problem of providing one-coatmaterials is aggravated because in order to obtain desired gloss,enamels are usually formulated with a low pigment content. Thus, theaddition of more pigment to provide a greater hiding power and makeenamels suitable for onecoat application results in loss of the desiredgloss. Moreover, addition of pigment to increase hiding power is onlyeffective to a certain degree. For example, in the case of white enamelsusing titanium oxide as the hiding pigment, 25 to 30% of pigment volumeconcentration produces maximum hiding, further addition results only ina decrease in hiding power and a great increase in viscosity.

A second approach that is often taken in order to increase hiding poweris to apply the paint to the surface in a thicker film. In order toaccomplish this, a means of applying a proper flow must be used. In anyevent, and most especially in brushing or rolling application, seriousproblems of proper flow and brushability of the paints arise. Thus, ifthe solids content of the paint is increased in order to achieve athicker film, the viscosity of the paint is increased and brushing ismade much more difficult. A common practice which is used in order toovercome these difficulties is the use of a thixotropic paint vehicle. Athixotropic paint will flow easily when rolling pressure is applied, butwill assume a gel structure when the pressure is removed, allowinggreater coat thicknesses. Means which have been used to impartthixotropic character to paints have been the use of certain additivesand the use of thixotropic alkyd resins as a vehicle. Among thematerials which have been used to modify the flow properties of paintare water; bodied oils, which are bodied just short of gelation, and actto raise the average vehicle viscosity; metallic soaps; certain acidicmaterials which form in situ soaps with basic pigments; silica pigments,which provide the effect of a flocculated structure; and colloidal-typeadditives, which swell in the vehicles to yield a colloidal structurewith thixotropic properties. The

ice

obvious advantage of a thixotropic paint is that it will have a lowviscosity under the shearing action of a brush and a high viscosity atrest. This effect results in a highly desirable combination ofproperties, particularly if the recovery from low to high viscosity isrelatively slow and the paint contains a solvent of low volatility.Under these conditions, the bulk consistency of the paint will be highenough to prevent dripping and splattering, but the paint will flow andspread easily under the shearing action of the brush. The return to highviscosity with removal of the brush shear prevents sagging and enhancesthe hiding power by permitting the application of a thick film.

It has now been found that paints possessing excellent brushability,hiding power, sag resistance, and high gloss retention maybe compoundedemploying as a non-volatile vehicle, a binary mixture of alkyd resins,the mixture comprising a combination of (A) a modified alkyd resinhaving an oil content between about 55 and 70 weight percent, and (B) asecond alkyd resin having an oil content of from to weight percent.

The preferred resins are the oil-modified glyceryl phthalate resins.These materials are polymeric polyesters of polyhydric alcohols havingmore than two hydroxyl groups, e.g., glycerol and the resinifyingpolycarboxylic acids which are phthalic acids and terephthalic acid. Aportion of the polycarboxylic acid is replaced by a fatty acid fromvegetable or marine oils to produce an oilmodified alkyd resin. Resinsmay be made with drying, semi-drying or non-drying oils. However, thedrying and semi-drying oils are preferred for the paints and vehicles ofthis invention. Oils which are commonly employed in the modification ofthe resins include the drying oils such as linseed and dehydrated castoroil, and the semi-drying oils such as soybean oil, etc. The modificationmay be made by employing selected fatty acids in the manufacture, ratherthan using the oil itself. The preparation of these modified resins iswell known in the art, there being numerous patents and otherpublications directed to the subject, and since the preparationcomprises no part of this invention, it will not be further elaborated.However, it may be noted that suitable alkyds include those whichcontain a wide variety of polyhydric alcohols, i.e., those other thanglycerol. For example, pentaerythritol is often used to replace part ofthe glycerol and to produce further modified characteristics in theresins. Thus, included among the polyfunctional alcohols which may beemployed are glycol, diethylene glycol, triethylene glycol, propyleneglycol, dipentaerythritol, sorbitol, mannitol, etc.

The non-volatile vehicles of the invention are prepared by simply mixingtogether the appropriate quantities of the desired resins and oil. Thepaints are prepared conventionally, with the provision that the resins,etc., must be mixed together either prior to or concurrently with theaddition of the other paint constituents, e.g., pigment, anti-skinningagents, drier, etc. Thus, it is not suitable for the pigment, etc. to beadded to each resin component and then the material mixed together. Thisprocedure will not produce the desired thixotropic properties.

The proper portions of the resin components (A) and (B) are from 5 to 30percent of (A) and, reciprocably, from 70 to percent by weight of (B).As will be shown, these proportions produce a vehicle that imparts tothe paint in which the vehicle is employed, surprisingly high sagresistance combined with excellent brushability of the paint.

In order to determine the properties of the vehicles in paints whichwere prepared, the following determinations were employed:

Viscosity of resin solutions (vehicles) The viscosity of resin solutionswas determined with the Zeitfuchs cross-arm viscometer. Thedetermination was made according to ASTM Method DT445-Test forKenesurface .irregularities. It depends primarily upon surface maticViscosity, Appendix F. The readings are given tension and viscosity ofthe paint during initial stages of directly in centistokes, which can beconverted to centidrying. A low viscosity paint under low-shearconditions poises by multiplying by the density.- will have goodleveling. Leveling is evaluated by the Paint viscosity, Krebs units 5method of the New York Paint Society. Reference to the I method may befound in New York Society for Paint The Krebs-Stormer viscosity IS themost commonly T hnolo Th Evaluation of Leveling by 3 Drawused scale forcomparing the viscosities of brushing Do n M th d, ()fli ial Digest ofth F d ti n of enamels. The Krebs-Stormer viscosimeter employs a two-Societies for Paint Techn l gy, -1435 (1960), A

bladed paddle immersed in the paint. Weights attached 10 cording to themethod, pairs of stripes of 5 different film to the paddle through apulley system cause the paddle t thicknesses are applied to a glassplate in a manner rotate- The Weight required to rotate the Paddle at200 similar to that used to evaluate sag resistance. The Howr-psproportional to the viscosity n Kr s n t ing together of the duplicatepaint stripes is a measure of (KU). leveling when the panels are allowedto dry in a hori- Brushability 1 zontal position. The paints are ratedon a scale where 0 Brushability in the art is the ease with which thebrush Poor and excellentcan be moved across to the surface while thepaint is Gloss being applied. It is thus a measure of the high shearviscosity of the paint, and this figure must be low for Gloss is theability of a dried paint film to reflect light good brushability. Inthis work the brushability was and to reflect images distinctly. Thedesired gloss will measured with a Brushometer, which is a viscosimetervary with the end use of the product, and its level depends operatingata high shear rate of about 20,000 sec.-1. mostly upon the inherentnature of the resin, the type and The instrument and methods ofoperation have been deamount of p gm n For the highest 8 however,scribed by Patton (Thomas C. Patton), A Modern Aplowest viscosity isrequired because the paint must'fiow proach to the Measurement andEvaluation of Brushsufficiently to cover all pigment particles and forma ability, Ofiicial Digest of the Federation of Societies for smoothsurface. Gloss is measured by means of the Paint Technology 36-745(1964). In the test the head of Gardner Gloss Meter, which is aphotoelectric device that the instrument is immersed in the paint. Thepaint is measures the percent of incandescent light reflected by shearedin the annular space between a rotating shaft the paint surface.

and a suspended cylinder, the torque transmitted from In order todemonstrate the outstanding characteristics the shaft through the paintto the cylinder is read fro a of the paints of this invention, paintswere prepared using dial d i proportional to h viscosity i poises. atwo-resin system and a comparable three-resin system of this invention.Table I below gives the compositions and properties of the resinsemployed. Alkyd resins and Sagging is the downward flow of paint thatresults in oils were prepared, employing the constituents in Table Sagresistance an uneven film thickness. It appears most often as cur- I, asfollows.

TABLE I.RESIN PROPERTIES Properties Resin 1 Resin 2 Resin 3 Resin 4Resin 5 Resin 6 Resin 7 Oil Type Tall oil fatty Tall oil fatty Tall oilfatty safflower Soya- Soya- Tall oil fatty acids. acids. acids.safilower. safllower. acids. Dibasic Acid Type Isophtlialic IsophtlialicIsophthalic Is0phthalic Phthalic Isophthulic.... Isophthalic. PolyolType Penta- Penta- Penta- Glycerol Pcnta- Penta-Pentaerythri'tolerythritolerythritol.erythritolerythritolcrytliritolglycerol. glycerol. glycerol. glycerol.glycerol. Plitlialie Conteiit,Wt. percent 23 21 14 22 25 0 23. OilCoiitciit,Wt. pcrccnt 67 71 c. 82 70 61 85 o6.

tains or tears on the painted surface. A painter Will Paints wereprepared employing the resin vehicles of most always adjust the amountof paint he is applying to Table I. These resin combinations wereblended together avoid sagging, thus a paint with low sag resistancewill before addition of pigment and other additives. The comusually hidepoorly. Sag resistance depends primarily on position of a typical paintis listed in Table II.

the low-shear viscosity of the paint during the initial stages ofdrying. Either the initial viscosity should be high, or it TABLEFORMULAS should rise rapidly during the first few minutes after appli-(loo-gallon batches) cation. Paint A (pounds) Sag resistance is measuredby applying a series of Resin 6 (85% oil length) 262.0

stripes of varying film thickness to a glass plate, placing the Resin 5(61% Oil length) 44.0

plate in a vertical position with the stripes horizontal, and Tio-rutile pigment 357.0

measuring the percent increase in width of the strips after CaCO pigment112.0

the paint has dried. This procedure is described in an Zinc oxide 12.5

article by D. J. Rassmussen and W. H. Ellis, The Aluminum stearate 4.0

Measurement and Control of Paint Sagging, Oflicial Lecithin 2.5

Digest Digest of the Federation of Societies for Paint Drier 6.5

Technology, 34-1104 (1962). Results are reported as the Anti-skinningagent 2.5

film thickness at 50% or 100% increase in stripe width. Odorless thinner207.0

Originally, the stripes are At-inch in width and flt-inch 65 apart. Thestripes are laid down with a metal blade, leaving 1,010.0

a wet film having a thickness of about one-half the clearance of theblade, and the results are easily reported in Vehicle solu is percentterms of blade clearance rather than actual wet film P VQ=(T.1O2= 2O,CaCO3= 10) thickness. The scale runs from a poor rating of 2 to anVehlcle vlscoslty=loo ccntlstokcs excellent ra g of 18- The brushabilityand sag resistant characteristics of the Leveling paints prepared, aswell as the viscosity characteristics of the resin pairs, weredetermined. It was found that at con- Leveling IS the ability of a paintto form a smooth film centrations of from about 5 to 30% by weight ofthe after pp lon d 0 e l ln te b ush arks and other lower oil contentresin in the higher, the sag resistance reaches a maximum; theBrushometer viscosity remains low, giving excellent brushingcharacteristics.

Thus, the maximum in sag resistance combined with good brushability isobtained with a first resin having an oil content of about 90% and aresin (Resin 1) having an oil content of about 55%, a point at whichinsolubility is approached. The appended figure shows the viscositiescaused by the interaction of three resin pairs. The table is read asweight percent of the first resin in a blend with the second resin. Itwill be noted that the maximum effect in this case is obtained withresin 5 in resin 6, the minimum with resin 4 in resin 6. The minimumdifference in oil content of the two resins thus must be at least 8percentage points in order to obtain the desired thixotropic propertiesof this invention. Further, it is necessary that the lower oil contentresin have an oil content lower than about 68% by weight and preferablynot more than 66% by weight. For example, a blend of a 71% oil contentresin (resin 2) with an 82% oil content resin (resin 3) gave substantiallinearity in viscosity over various combinations, while the combinationof a 67% oil content resin (resin 1) with an 82% oil content resin gavea substantial thixotropic eflfect, and combinations with a 66% oilcontent resin (resin 7) with the 82% oil content resin gave asubstantially greater efiect. The higher oil content resin should nothave an oil content greater than about 90%.

The paints of this invention are prepared in the same manner as anyoil-based paint; the techniques for preparation are well known in theart and will not be elaborated upon here.

While the preferred paints of this invention are gloss enamels, sincethe non-sag characteristics and gloss retention imparted by the vehiclesare most important for these paints, the need for one-coat materialsmakes these vehicle combinations suitable for many other types of paint,such as fiat enamels, outdoor housepaints of various types, and, infact, any type of oil-based paint.

In addition to the pigments employed, other normally used paintadditives are often employed in the paints of the invention, such asdrying agents, extenders, corrosion inhibitors, etc.

We claim:

1. An oil-based, thixotropic paint having as a nonvolatile vehicle, amixture of from 5 to 30% by weight of (A) a modified alkyd resin havingan oil content of to 67 weight percent, and from 70 to percent by weightof (B) a second modified alkyd resin having an oil content of from 70 to90 weight percent, wherein there is a differenceof oil content between(A) and (B) of at least 8 weight percent, and wherein (A) and (B) arepolyhydric alcohol phthalate resins modified by fatty acids from dryingoils or semi-drying oils.

2. The paint of claim 1, wherein (A) is present in the amount of fromabout 10 to 25 weight percent.

3. The paint of claim 2 wherein the difference in oil content between(A) and (B) is at least 20 weight percent.

4. The paint of claim 1 wherein (A) is a resin having an oil content offrom about 57 to 66 weight percent and (B) is a resin with an oilcontent of about 85 weight percent.

5. The paint of claim 1 in which (A) and (B) are glyceryl phthalate.

6. The paint of claim 1 in which (A) and (B) pentaerythritol modifiedglyceryl phthalate resins.

7. A thixotropic, non-volatile paint vehicle comprising a mixture asdefined in claim 1.

8...A paint vehicle comprising a mixture as defined in claim 2.

are

References Cited UNITED STATES PATENTS 2,232,426 2/ 1941 Barrett 260222,279,496 4/ 1942 Sackett 26022 2,287,986 6/ 1942 Gowing et a1. 260222,889,293 6/ 1959 Hensley et al 26022 3,077,459 2/ 1963 Hershey et a1.26022 OTHER REFERENCES Rinse, Paint Technology, November 1946, vol. XI,No. 131, pages 429 and 430.

Trimellitic Anhydride, published 8 by Amoco Chemicals Corp., pages10-23.

DONALD E. CZAJA, Primary Examiner R. W. GRIFFIN, Assistant Examiner US.Cl. X.R.

